Maybe we should institute an Older Americans Overtreatment of the Month award. Picking a winner might be a tough task, though.

The latest candidate: everyone’s favorite screening test, the colonoscopy, which allows doctors to spot and then remove growths called polyps that can evolve into colon cancer. Routine screening has probably contributed to the declining death rate from that disease, considered highly curable in its early stages, and it’s still underused, particularly among members of racial and ethnic minorities and the uninsured.

“This is truly mindless application of guidelines that were developed for 50-year-olds,” said Dr. James Goodwin, a geriatrician at the University of Texas Medical Branch and lead author of the study, published this month in The Archives of Internal Medicine.

For years, the recommendations for screening colonoscopies (as opposed to those performed because of a specific symptom) have been virtually unanimous. Medical authorities agree that people over age 50 should have one. Patients with negative results and no subsequent symptoms or indications don’t need another one for 10 years. “It takes a long time for polyps to evolve into cancer,” Dr. Goodwin said.

But in the Texas researchers’ sample — more than 24,000 Medicare enrollees who had a negative colonoscopy from 2001 to 2003 — more than 46 percent underwent a repeat colonoscopy in less than seven years. In fact, many of these tests took place after just three years or five. Yet in almost a quarter of all these repeat colonoscopies — 23.5 percent — the researchers, scrutinizing the medical records, could find no reason for performing them so soon.

Dr. Goodwin was especially troubled by the fact that a third of patients who were older than 80 when they had initial colonoscopies received another within seven years. The United States Preventive Services Task Force recommends no routine colon cancer screening for those older than 75, and no screening at all for those over age 85.

Preparation for a colonoscopy, merely unpleasant for most of us, can take a steep physical toll on the very old. They can become incontinent, setting off a cycle of prescriptions for drugs to stop diarrhea and then constipation. The preparations can disrupt eating and sleep. “It can throw people off for a long time,” Dr. Goodwin said.

“It would be a very bad idea for people with moderate dementia,” he added, and that’s a significant proportion of the 85-plus population. They may not understand the test’s purpose or be able to comply with the prep directions. Even more to the point, people with dementia, a terminal disease, are unlikely to live long enough to benefit from colon cancer screening.

The researchers also found that older patients with three or more health problems — like heart failure, high blood pressure, chronic bronchitis and asthma — had even higher rates of repeat colonoscopies without medical indications. “That’s bizarre,” Dr. Goodwin said. With multiple diseases, “you’re less likely to live long enough to develop colon cancer. You should be less likely to be screened.”

Fortunately, the rate of complications from colonoscopy is low: one Medicare patient in 1,000 requires hospitalization, and one in 10,000 dies. “It’s a small number, which is dwarfed by the cancers you can prevent,” Dr. Goodwin said. “But if you double the rate of screening, you double the complications and deaths, without any benefit to patients.”

So why does this happen? At about $1,000 per procedure, there’s clearly an economic incentive, Dr. Goodwin said. But patients and their families bear some responsibility as well.

“We’ve done too good a job with some of these messages” urging tests for various diseases, he said. “Some of the demand comes from patients who don’t understand that there’s a cost to these things, and I don’t mean the economic cost.” But the expense is an outrage, too. Medicare supposedly reimburses for screening colonoscopies only every 10 years, but it denied only 2 percent of the claims in this study.

Noted. A key question for seniors and their caregivers to lob at doctors: What’s the reason for this colonoscopy when routine screening isn’t recommended for someone this age? (That is, a patient older than 75.)

Sometimes, of course, there’s a valid explanation. When there’s not, said Dr. Goodwin, “even if you had a rabid doctor who just loved to do colonoscopies, that question would give him pause.”

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About

Thanks to the marvels of medical science, our parents are living longer than ever before. Most will spend years dependent on others for the most basic needs. That burden falls to their baby boomer children. The New Old Age blog explored this unprecedented intergenerational challenge. Paula Span will continue to write New Old Age columns twice monthly at nytimes.com/health and the conversation will continue on Twitter (@paula_span) and Facebook.